DHEA
Dehydroepiandrosterone (DHEA) and its sulfated form, dehydroepiandrosterone-sulfate (DHEAS) are the principal circulating steroids in humans. These two steroids are synthesized in the adrenal cortex and are normally found at about a 1:1000 molar ratio in serum. DHEAS is thought to be the storage form of DHEA, and can be converted to DHEA by the action of a sulfatase. DHEA can serve as a substrate for the production of androgenic steroids, both in the steroidogenic organs (adrenal glands, gonads and placenta) and in peripheral tissues, such as the skin, liver and brain.
DHEA is synthesized from pregnenolone in a two step reaction by cytochrome P450c17 (CYP17). CYP17 has both 17.alpha.-hydroxylase activity (which converts pregnenolone into 17.alpha.-hydroxypregnenolone, which is a cortisol precursor) and 17,20-lyase activity (which converts 17.alpha.-hydroxypregnenolone to DHEA). Purified CYP17 has very low 17,20-lyase activity. However, addition of cytochrome b5 enhances the 17,20-lyase activity of cytochrome P450c17, resulting in increased production of DHEA from pregnenolone and decreased production of cortisol (Katagiri et al. (1995) Arch. Bioch. Biophys. 317(2):343-347). IGF-I has been reported to increase transcription of the CYP17 gene in cultured Leydig cells, although expression of the 313-hydroxysteroid dehydrogenase gene (which encodes an enzyme involved in the conversion of DHEA into androgenic steroids and 17.alpha.-hydroxypregnenolone into cortisol) was not affected. Insulin-like growth factor I (IGF-I) also increases choriogonadotropin-stimulated production of testosterone by Leydig cells (Chuzel et al. (1996) Eur. J. Biochem. 239:8-16).
DHEA and DHEAS levels normally peak in the second or third decade of life, declining by 80% or more of peak levels by age 70. Low levels of DHEA and DHEAS are associated with a variety of disease conditions, including Alzheimer's Disease and cardiovascular disease. U.S. Pat. No. 5,527,789 to Nyce suggests that high levels of DHEA (such as those caused by administration of DHEA or DHEAS) can cause cardiovascular disease due to depletion of cardiac ubiquinone, but Aberg et al. ((1996) Chem. Biol. Interact. 99(1-3):205-218) shows that cardiac ubiquinone levels are unaffected by DHEA administration.
DHEA and its derivatives have been described as treatments for a wide variety of conditions, including memory dysfunction, prostatic hypertrophy, immune dysfunction, alopecia, for inhibiting platelet aggregation, and minor and major depression as well preventatives for cancer and cardiovascular disease (U.S. Pat. Nos. 4,835,147, 5,077,284, 5,407,684, 5,162,198, 5,407,927, and 5,527,789 and International Patent Application No. WO 94/16709). DHEA is also known to increase REM sleep in rats and humans, suggesting its utility for the treatment of sleep disorders,, memory loss and age-related dementia (Robel and Baulieu (1995) Ann. NY Acad. Sci. 774:82-110).
Administration of DHEA has been reported to increase serum levels of IGF-I (U.S. Pat. No. 5,407,927; Morales et al. (1994) J. Clin. Endocrinol. Metab. 78(6):1360-1367) and to increase the sense of well-being, but not the libido, of subjects receiving DHEA. However, these reports do not establish any linkage between the elevation of IGF-I levels and an improved sense of well-being.
Direct administration of DHEA, DHEAS and their derivatives can lead to serious side effects. For example, acne, hair loss, hirsutism and deepening of the voice have been reported with use of DHEA in women. In men, excess DHEA may stimulate the growth of prostatic cancer. Thus, gratuitous addition of these steroid hormones individually to the circulation has been shown to be complicated in practice. Direct administration of pharmacological amounts of DHEA and/or DHEAS may cause a hormonal imbalance, which may in turn cause the side effects associated with DHEA and DHEAS administration.
Thyroid hormones
The thyroid hormones, triiodothyronine (T3) and tetraiodothyronine (T4) are major metabolic regulators in mammals. T4 is less active than T3, and can be converted to T3 in peripheral tissues. Administration of T4 or T3 increases metabolism, erythropoiesis, bone turnover and the rate of muscle relaxation. Although thyroid hormones increase the rate of protein synthesis, hyperthyroidism is associated with weight loss and muscle wasting. Hypothyroidism can be accompanied by lethargia, decreased pulmonary function (hypoventilation), low cardiac output, and decreased renal output. The thyroid hormones also interact with other endocrine hormones, including the growth hormone axis and steroidal hormones.
T4 and T3 are synthesized from thyroglobulin, a protein that is iodinated on its tyrosine residues. Two iodinated tyrosines are condensed to form a molecule of T4 or T3. Thyroglobulin, which is stored extracellularly in the follicular lumen of the thyroid gland, acts as a storage molecule for the iodinated tyrosine residues. Iodinated tyrosine residues are released from thyroglobulin by intracellular proteolysis in thyroid cells. IGF-I has been shown to increase transcription of thyroglobulin in FRTL-5 (rat thyroid) cells (Kamikubo et al. (1990) Mol. Endocrinol., 4:2021-2029). The influence of increased levels of thyroglobulin mRNA on T4 and T3 levels is, however, unknown.
IGF
IGF-I and IGF-II are growth factors that have related amino acid sequence and structure, with each polypeptide having a molecular weight of approximately 7.5 kilodaltons (Kd). IGF-I mediates the major effects of growth hormone, and thus is the primary mediator of growth after birth. IGF-I has also been implicated in the actions of various other growth factors, since treatment of cells with such growth factors leads to increased production of IGF-I. In contrast, IGF-II is believed to have a major role in fetal growth. Both IGF-I and IGF-II have insulin-like activities (hence their names), and are mitogenic (stimulate cell division) and/or are trophic (promote recovery/survival) for cells in neural, muscular, reproductive, skeletal and other tissues.
Unlike most growth factors, IGFs are present in substantial quantity in the circulation, but only a very small fraction of this IGF is free in the circulation or in other body fluids. Most circulating IGF is bound to the IGF-binding protein IGFBP-3. IGF-I may be measured in blood serum to diagnose abnormal growth-related conditions, e.g., pituitary gigantism, acromegaly, dwarfism, various growth hormone deficiencies, and the like. Although IGF-I is produced in many tissues, most circulating IGF-I is believed to be synthesized in the liver.
IGF is known to bind to at least three different cellular receptors; the type 1 IGF receptor, the type 2 IGF receptor, and the insulin receptor (to which IGF binds with much lower affinity than the type 1 or 2 receptor). Mutants of IGF-I have been described which have altered binding to one or more of these cellular receptors. Mutations at residue 24 (normally tyrosine) to non-aromatic residues or replacement of residues 28-37 selectively affects binding to the type 1 receptor, while mutations at residues 49-51 can selective reduce type 2 receptor binding. Mutations at residue 60 (from tyrosine to non-aromatic amino acids) can alter binding to the type 1 and 2 IGF receptors as well as the insulin receptor (Cascieri et al. (1988) Biochemistry 27:3229-3233; Cascieri et al. (1989) J. Biol. Chem. 264:2199-2202; Bayne et al. (1988) J. Biol. Chem. 264:11004-11008; Bayne et al. (1990) J. Biol. Chem. 265:15648-15652).
Almost all IGF circulates in a non-covalently associated ternary complex composed of IGF-I or IGF-II, IGFBP-3, and a larger protein subunit termed the acid labile subunit (ALS). The IGF/IGFBP-3/ALS ternary complex is composed of equimolar amounts of each of the three components. ALS has no direct IGF binding activity and appears to bind only to the IGF/IGFBP-3 binary complex. The IGF/IGFBP-3/ALS ternary complex has a molecular weight of approximately 150 Kd. This ternary complex is thought to function in the circulation "as a reservoir and a buffer for IGF-I and IGF-II preventing rapid changes in the concentration of free IGF" (Blum et al., pp. 381-393, MODERN CONCEPTS IN INSULIN-LIKE GROWTH FACTORS (E. M. Spencer, ed., Elsevier, N.Y., 1991).
Some mutant IGF-Is exhibit altered binding to IGFBP-3 and/or alterations in the ability to form the ternary complex. For example, mutations at residues 3, 4, 8, 9, 12, 15, 16 and 24 (B domain mutants) and mutations at residues 49-51 reduce formation of the binary complex, while mutations involving residues 55 and 56, as well as IGF-I where residues 63-70 (1-62 IGF-I) were deleted or residues 28-37 were replaced with a Gly.sub.4 linker (1-27-Gly.sub.4 -38-70 IGF-I) or where both changes were made (1-27-Gly.sub.4 -38-62 IGF-I)) and mutants thereof (for example, 1-62 IGF-I where residue 24 was also changed) actually have increased binding to IGFBP-3. Some of these mutants, particularly the 1-62 IGF-I with a mutation at residue 24, have a reduced capacity for formation of the ternary complex, even though formation of the binary complex is increased (Baxter et al. (1992) J. Biol. Chem. 267:60-65).
Nearly all of the IGF-I, IGF-II and IGFBP-3 in the circulation is in complexed form, so very little free IGF is detected. Moreover, a high level of free IGF in blood is undesirable. High blood levels of free IGF would lead to serious hypoglycemia due to the insulin-like activities of IGF. In contrast to the IGFs and IGFBP-3, there is a substantial pool of free ALS in plasma which assures that IGF/IGFBP-3 complex entering the circulation immediately forms the ternary complex.
IGFBP-3 is the most abundant IGF binding protein in the circulation, but at least five other distinct IGF binding proteins (IGFBPs) have been identified in various tissues and body fluids. Although these proteins bind IGFs, they each originate from separate genes and have unique amino acid sequences. Thus, the binding proteins are not merely analogs or derivatives of a common precursor. Unlike IGFBP-3, the other IGFBPs in the circulation are not saturated with IGFs. Moreover, none of the IGFBPs other than IGFBP-3 can form the 150 Kd ternary complex.
IGF-I and IGFBP-3 may be purified from natural sources or produced by recombinant means. For instance, purification of IGF-I from human serum is well known in the art (Rinderknecht et al. (1976) Proc. Natl. Acad. Sci. USA 73:2365-2369). Production of IGF-I by recombinant processes is shown in EP 0 128 733, published in December of 1984. IGFBP-3 may be purified from natural sources using a process such as that shown in Baxter et al. (1986, Biochem. Biophys. Res. Comm. 139:1256-1261). Alternatively, IGFBP-3 may be synthesized by recombinantly as discussed in Sommer et al., pp. 715-728, MODERN CONCEPTS OF INSULIN-LIKE GROWTH FACTORS (E. M. Spencer, ed., Elsevier, N.Y., 1991). Recombinant IGFBP-3 binds IGF-I in a 1:1 molar ratio.
Topical administration of IGF-I/IGFBP-3 complex to rat and pig wounds is significantly more effective than administration of IGF-I alone (Id.). Subcutaneous administration of IGF-I/IGFBP-3 complex to hypophysectomized, ovariectomized, and normal rats, as well as intravenous administration to cynomolgus monkeys, "substantially prevents the hypoglycemic effects" of IGF-I administered alone (Id.).
IGF has been proposed as a treatment for a wide variety of indications. U.S. Pat. Nos. 5,434,134, 5,128,320, 4,988,675, 5,106,832, 5,534,493, 5,202,119 and 5,273,961 and have disclosed the use of IGF for the treatment of cardiomyopathy and myocardial infarction, steroid-induced catabolism, type II (insulin resistant) diabetes, renal disorders, pancreatic disorders, for increasing humoral immune response and for prevention of acute renal failure, respectively. Additionally, European Patents Nos. EP 434 625, EP 436469 and EP 560 723 and International Patent Applications Nos. WO 93/23071, WO 91/12018, WO 92/00754, WO 93/02695 and WO 93/08826 disclose the use of IGF for the treatment of bone disorders, type I juvenile or insulin-responsive) diabetes and gastrointestinal disorders.
The use of IGF complexed with IGFBP-3 has also been described for use in the treatment of a variety of conditions. U.S. Pat. Nos. 5,200,509, 5,187,151, 5,407,913, and 5,527,776 disclose the use of IGF/IGFBP-3 complex for the treatment of osteoporosis, for inducing an anabolic state when given by subcutaneous bolus injection, for increasing tissue repair when given systemically, and for treating anemia. International Patent Applications Nos. WO 95/03817, WO 95/08567, WO 95/13823, WO 95/13824, WO 96/02565 disclose the use of IGF/IGFBP-3 complex for the treatment of disorders of the reproductive, immunologic, neural, renal, and skeletal systems.
In addition to its activities in other organ systems, IGF has trophic effects on the cells of the peripheral and central nervous system. IGF's trophic effects on neural cells include promoting the survival of a variety of neuronal cell types as well as promoting neurite outgrowth in motor neurons. U.S. Pat. Nos. 5,093,317, 5,420,112, 5,068,224, and International Patent Applications Nos. WO 93/02695, WO 93/08826 and WO 95/13823 describe the use of IGF or IGF complexed to IGFBP-3 for the treatment of disorders of the nervous system, exploiting IGF's trophic activity on the cells of nervous tissues. None of these patents or publications disclose or suggest the use of IGF for the treatment of psychological disorders or memory loss.
Other disorders exist which would benefit from a reduction in the levels of IGF. For example, some cancer cells are dependent on IGF for continued survival (Resnicoff et al. (1994) Cancer Res. 54:2218-2222). Reduction in circulating IGF levels could result in tumor progression, as IGF-dependent tumor cells undergo apoptosis. In autoimmune disorders, reduction in IGF levels could reduce symptoms of these disorders, as IGF is known to have stimulatory effects on the immune system.
None of the references disclosed above disclose or suggest the use of IGF or IGF/IGFBP-3 complex for the treating or alleviating the symptoms of psychological or metabolic disorders. Further, none of the cited references disclose or suggest the administration of IGF or IGF/IGFBP-3 complex for treating or alleviating the symptoms of sleep disorders or for treating or alleviating symptoms and disorders associated with sexual senescence.
Psychological Disorders
The acuity of memory gradually declines with age, and can also be affected by a variety of disorders. Memory can be characterized in various ways, including declarative or explicit (involving recall and recognition) versus implicit (involving skills and conditioning). A number of compounds have been suggested as treatments for enhancing memory, including cholinergic agonists and cholinesterase inhibitors, calcium channel blockers, angiotensin convertring enzyme (ACE)-inhibitors such as captopril and peptides such as vassopressin and corticotropin (which induce the synthesis of adrenal steroids), and others (Mondadori et al. (1994) Proc. Natl. Acad. Sci. USA 91: 2041-2045). Steroid hormones have also been used to treat memory loss. Administration of pregnenolone sulfate (PS), dehydroepiandrosterone sulfate (DHEAS), androstenedione (A), testosterone and aldosterone (among others) were effective in improving retention in a rodent model (Flood et al. (1992) Proc. Natl. Acad. Sci. USA 89: 1567-1571). PS and DHEAS were active as memory enhancers when injected into the hippocampus. PS was also active when injected into the amygdala and mammillary bodies but not the caudate nucleus (Flood et al. (1995) Proc. Natl. Acad. Sci. USA 92: 10806-10810). Pregnenolone and DHEA are believed to act in a paracrine fashion at neurons, thus modifying sleep EEG in humans in a manner that suggests their potential as memory enhancers (Holsboer et al. (1994)Ann. NY Acad. Sci. 746: 345-361).
IGF-I has been shown to induce long term depression of glutamate-induced gamma-aminobutyric acid release in the cerebellum (Castro-Alemancos et al. (1993) Proc. Natl. Acad. Sci. USA 90: 7386-7390). This finding led Castro-Alemancos et al. to test the effects of IGF-I on motor learning and retention (i.e., implicit memory), using the "eye-blink response" as the indicator. Experimental results led them to postulate that IGF-I plays a role in learning the eye-blink response but they found no evidence for a role for IGF-I in retention or memory (Castro-Alemancos et al. (1994) Proc. Natl. Acad. Sci. USA 91: 10203-10207).
There is a need in the art for an effective method for enhancing memory and for treating and/or alleviating the symptoms of memory loss.
Depressive disorders are common among the population. Seventeen percent of the population is expected to suffer from major depression during their lifetime prevalence (Andrews et al. (1994) Am. J. Med. 97:24S-32S). Approximately two-thirds of patients respond to antidepressant medication. Nevertheless, all effective classes of antidepressants have significant side-effect profiles. Selective serotonin reuptake inhibitors (SSRIs) cause nausea, headache and sexual dysfunction.
Additionally, many SSRIs inhibit a number of hepatic cytochrome P450 isozymes which can lead to serious drug interaction problems in addition to the side effects caused directly by the drugs themselves. Tricyclics are cardiotoxic and overdoses are frequently fatal. Other classes can cause seizures, priapism and elevations in blood pressure (Andrews et al. (1994) Am. J Med. 97: 24S-32S).
Primary hypothyroidism is a relatively common endocrine disorder that develops insidiously and can mimic depression. Between and 8 and 14 percent of patients diagnosed with depression have some degree of hypothyroidism (Tallis (1993) Brit. J. Clin. Psychol. 32:261-270). Primary hypothyroidism may be treated by increasing levels of T4 and/or T3.
There is a need in the art for a method for treating and/or alleviating the symptoms of depression of multiple etiologies.
Metabolic Disorders
Spinal chord injury (SCI) in adult males may result in various hormonal and metabolic abnormalities--both as a result of injury and secondary to reduced exercise and mobility. Various studies in this patient population have documented the following abnormalixties in subjects with SCI relative to the normal population:
a suppression in the GH response to growth hormone releasing hormone (GHRH), arginine or other agents; significantly lower IGF-I levels; elevated follicle stimulating hormone (FSH) and leutinizing hormone (LH) levels; reduced thyroid hormone levels; hyperprolactinemia (in quadriplegics only); hypogonadism associated with lowered testosterone levels; increased frequency of urinary tract infections; obesity; high prevalence of carbohydrate intolerance; diabetes; low HDL cholesterol; lowered cardiopulmonary fitness and dyspnea at rest; increased susceptibility to coronary artery disease; deficient bowel control (esp. constipation); lower resting metabolic rate; and active pressure sores (Shetty et al. (1993) Am J. Med Sci. 305:95-100; Huang et al. (1995) Metabolism 44:1116-20; Tsitouras et al. (1995) Horm. Metab. Res. 27:287-292; Geders et al. (1995) Am. J. Gastroenterol 90:285-289; Bauman et al. (1994) Metabolism 43:749-756; Bauman et al. (1994) J. Clin. Endocrinol. Metab. 78:1135-1138; Almenoff et al. (1995) Paraplegia 33:274-277; Bauman et al. (1994) Horm. Metab. Res. 26:152-156; Kahn et al. (1996) Proc.Natl.Acad.Sci. USA 93:245-249).
Atelectasis (insufficient lung inflation/deflation) and pneumonia are the major causes of morbidity and mortality in patients with SCI (cited in Almenoff et al., supra). In a study of 165 SCI subjects, forced vital capacity and other measures of pulmonary function were inversely correlated with with the level of injury (i.e., the higher the level of injury, the lower the parameter; Almenoff et al. (1995) Lung 173:297-306). Other studies have shown that thyroid hormone (both T3 and T4) levels are significantly lower in quadriplegics than in paraplegics or normal subjects (Huang et al., supra). Thyroid hormone levels are correlated with pulmonary function. Further, hypothyroid individuals are known to suffer from breathing difficulties.
Most of the metabolic abnormalities experienced by SCI victims are also increasingly observed during the normal aging process in humans. For this reason, SCI may provide an excellent model for the study of the normal aging process as well as premature aging (Bauman et al. (1994) Horm. Metab. Res., supra). There are also several genetic diseases which cause premature aging, including ataxia telangiectasia, Werner's syndrome, Hutchinson-Guilford progeria, and Cockayne's syndrome. It is expected that symptoms that are shared between SCI, aging and premature aging would benefit from the same treatment.
Accordingly, there is a need in the art for an effective treatment for alleviating symptoms associated with SCI and for the symptoms of aging and premature aging.
Stress hormones can profoundly affect the workings of all endocrine subsystems, resulting in a condition referred to as hypothalamic-pituitary axis dysregulation (HPA dysregulation). For example, individuals under stress do not experience the normal increase in growth hormone levels following induction of hypoglycemia (induced by administration of insulin); instead, IGF-I levels drop and cortisol and norepinephrine levels rise (Ferraccioli et al. (1994) J. Rheumatol. 21:1332-1334). This abnormal response is believed to play a role in lowering IGF-I levels in chronically stressed conditions such as fibromyalgia (Id.). Fibromyalgia is a relatively common disorder with a prevalence in the general population of between 2 and 4% (Wolfe et al. (1990) Arthritis Rheum. 33:160-172).
Fibromyalgia, which is approximately twice as common in women as in men, is characterized by widespread pain, tenderness, fatigue, sleep disturbance, paresthesias, anxiety, and other similar symptoms. Fibromyalgia has many symptoms in common with chronic fatigue syndrome and the two conditions are frequently treated with the same drugs. Interestingly, while sleep disturbances are associated with fibromyalgia, sleep deprivation itself can induce the symptoms of fibromyalgia (Moldofsky et al. (1975) Psychosom. Med. 37:341-351).
Physical and psychological stressors elevate plasma levels of IL-6. The source of this IL-6 is unknown, but it has been shown to be non-immune (Zhou et al. (1993) Endocrinol. 133:2523-2530). DHEAS has been shown to reduce chronically elevated levels of IL-6 (Daynes et al. (1993) J. Immunol. 150:5219-5230).
HPA dysregulation is also observed when sleep patterns are disrupted. Melatonin inhibits the basal and stimulated release of hypothalamic vassopressin in vitro (Yasin et al. (1993) Endocrinol. 132:1329-1336), and sleep inhibits activation of adrenocorticotropic hormone (ACTH) and cortisol secretion. Conversely, through the mineralocorticoid (slow wave sleep) and glucocorticoid (rapid eye movement--REM--sleep) receptors, cortisol can exert feedback effects on sleep patterns (Holsboer et al. (1994) Ann. N. Y Acad. Sci. 746:345-361). DHEA affects the duration of REM sleep and this may explain some of its actions on the consolidation of memory.
There is a need in the art for effective methods for treating disorders associated with chronic stress and/or alleviating the symptoms of disorders associated with chronic stress.
The thalassemias are a group of genetic diseases which share the symptom of reduced levels of hemoglobin in the blood (i.e., anemia). This is due to reduced or absent production of either adult alpha or adult beta hemoglobin. The existence of thalassemia in a subject emerges during the first month of life, as fetal hemoglobin is down regulated and adult hemoglobin is up regulated. Thalassemic individuals are unable to switch over to adult hemoglobin and become anemic and dependent on transfusions. In addition to anemia, thalassemia patients also experience symptoms relating to high levels of toxic products such as iron and billrubin. Animal models, including naturally occurring mutants and introduced mutants, are available for testing treatments for beta thalassemias (Popp et al. (1984) Proc. NY Acad. Sci. 445:432-444; Ciavatta et al. (1995) Proc. Natl. Acad. Sci. USA 92:9259-9263; Yang et al. (1995) Proc. Natl. Acad. Sci. USA 92:11608-11612). A need exists in the art for effective methods for improving or alleviating symptoms associated with deficiencies of detoxification in thalassemia patients.
Sexual Senescence
The hypothalamic-pituitary-gonadotropic axis is responsible for the proper function of reproductive organs as well as for some aspects of reproductive behavior. Although IGF-I has been implicated in gamete formation, little is known about its effects on sexual behavior. IGF-I has been implicated in the gonadotropic axis in a study of Igf1 knock-out mice, which are infertile dwarfs with drastically reduced levels of serum testosterone (Baker et al. (1996) Mol. Endocrinol. 10:903-918).
Androgen levels are known to decrease with aging in men. Androgen deficiency in men has been linked to decreased muscle mass, asthenia, osteoporosis and decreased sexual activity and, in some cases, changes in mood and cognitive function. In women, studies have reported a relationship between the transition into menopause and a decline in sexual interest and activity as measured by a variety of symptoms. Estrogen can affect some (but not all) of these symptoms (Nathorst-Boos et al. (1993) Acta Obstet. Gynecol. Scand. 72:656-660). In one study, McCoy Sexual Rating score (which relates to parameters such as the frequency of sexual fantasies, impaired lubrication and pleasure from intercourse) correlated with levels of circulating IGF-I (Nathorst-Boos et al. (1993) J. Psychosom. Obstet. Gynaecol. 14:283-293).
DHEA and its derivatives have been suggested as treatments for some symptoms of sexual senescence, such as prostatic hypertrophy and sexual dysfunction associated with menopause. U.S. Pat. No. 4,835,147 teaches the administration of DHEA for the treatment of prostatic hypertrophy and sexual dysfunction symptoms related to nervous system dysfunction.